Solid-liquid separation clarification

The nature and sizing of equipment depends on the economic values and proportions of the phases as well as certain physical properties that influence relative movements of liquids and particles. Pressure often is the main operating variable so its effect on physical properties should be known. Table 11.1 is a broad classification of mechanical processes of solid-liquid separation. Clarification is the removal of small contents of worthless solids from a valuable liquid. Filtration is applied to the recovery of valuable solids from slurries. Expression is the removal of relatively small contents of liquids from compressible sludges by mechanical means. 

The solid-liquid separation of shinies containing particles below 10 pm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as concentrated slurry. Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 xm in size. Dead end membrane microfiltration, in which the particle-containing fluid is pumped directly through a polymeric membrane, is used for the industrial clarification and sterilisation of liquids. Such process allows the removal of particles down to 0.1 xm or less, but is only suitable for feeds containing very low concentrations of particles as otherwise the membrane becomes too rapidly clogged.2,4,8... 

Flocculation or clarification processes are solids-liquid separation techniques used to remove suspended solids and colloidal particles such as clays and organic debris from water, leaving it clear and bright. Certain chemicals used (such as alums) also exhibit partial dealkaliz-ing properties, which can be important given that the principal alkaline impurity removed is calcium bicarbonate—the major contributory cause of boiler and heat exchanger scales (present in scales as carbonate), although closely followed by phosphate. 

Svarovsky L (2000), Gravity clarification and thickening, In Svarovsky L (ed), Solid-Liquid Separation, Butterworth-Heinemann, Oxford. 

Costaz et al. investigated the simultaneous electroflotation and disinfection of sewage in the presence of chloride ions (used to form hypochlorite ions) [140]. The solid-liquid separation was improved, compared with static clarification alone. The disinfection efficiency of the sludge was equal to or better than that obtained using gaseous clorine only. 

The PAC activated slndge system is a modified activated sludge process. PAC is added to the aeration tank where it is mixed with the biological solids. The mixed liquor solids are settled and separated from the treated effluent in a gravity clarifier. Polyelectrolyte will normally be added prior to the clarification step to enhance solids-liquid separation. If phosphorus removal is necessary, alum is often added at this point. Even with polyelectrolyte addition, tertiary filtration is normally required to reduce the level of effluent suspended solids. The clarifier nnderflow solids are continuously returned to the aeration tank. A portion of the carbon-biomass mixture is wasted periodically to maintain the desired solids inventory in the system. 

Fouthly, there are some major revisions or total rewrites such as Introduction to Solid-Liquid Separation, Gravity Clarification and Thickening, Vacuum Filtration, Centrifugal Filtration and Countercurrent Washing. 

Operating parameters such as SET, dissolved oxygen (DO), MLSS, sludge volume index (SVI), suspended solids removal. The two last parameters are important in CAS processes where secondary clarification is employed for the solids/liquid separation (Rossine/a/., 1982 Santos and Judd, 2010 Sterritt and Lester, 1981). 

Pharmaceutical Removal of suspended matter is a frequent application for MF. Processes may be either clarification, in which the main product is a clarified liquid, or solids recovery. Separating cells or their fragments from broth is the most common application. Clarification of the broth in preparation for product recovery is the usual objective, but the primary goal may be recovery of cells. Cross-flow microfiltration competes w l with centrifugation, conventional filtration by rotary vacuum filter or filter press and decantation. MF delivers a cleaner permeate, an uncontaminated, concentrated cell product... 

They are best suited to liquid-liquid separations and clarification duties, but not high solids concentrations due to the limited solids hold-up capacity. They can handle small-density difference separations and best suited to batch processes. They are difficult to clean, and as large-scale laboratory units, best avoided unless another type of centrifuge design will not work. 

These versatile machines are used for liquid clarification, concentration of light slurries, and liquid-liquid separation. They are capable of continuous operation even with high solids concentrations, since the solids phase can be discharged periodically if desired. They can also be arranged as hermetically sealed units for handling hazardous materials or in sterile applications. 

Hydroclones were introduced in 1891 to remove sand from water. They function like a gas-solid cyclone, have no moving parts, and rely on centrifugal force for separation, clarification, and dewatering processes. Hydroclones find use in concentrating slurries, in classifying solids in liquid suspensions, and in washing solids. They may be used alone or in conjunction with clarifiers, thickeners, or filters (Besendorfer, 1996). 

The conversions mentioned above are to be avoided whenever possible, because of inherent errors in such procedures, by using a method that would give the desired type of distribution directly. Different methods give different types of distributions and the selection of a method should be done on the basis of both the particle size and the type of distribution required. In common processing applications, for example, solid-fluid separations, it is the size distribution by mass that is usually of interest, because the separation efficiency is based on gravimetric means. There are, however, cases such as liquid clarification where turbidity of the overflow is of importance, and size distribution by surface or even by number would be more relevant. Figure 2.23 shows the four types of distribution in a diagram. 

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